Means for controlling the tension of a web



April 4, 1967 M. A. JEANS MEANS FOR CONTROLLING THE TENSION OF A WEB 2Sheets-Sheet 1 Filed March 5, 1965 mm NM Q .Q N

A ril 4, 1967 M. A. JEANS 3,312,415

MEANS FOR CONTROLLING THE TENSION OF A WEB Filed March 5, 1965 2Sheets-Sheet 2 MM: MM 2 2m 3y 41m a: filyl l- United States PatentOfiice 3,312,415 Patented Apr. 4, 1 967 3,312,415 MEANS FOR CONTROLLINGTHE TENSION OF A WEB Michael Anthony Jeans, Dorking, Surrey, England,as-

signor to The Printing, Packaging and Allied Trades ResearchAssociation, Leatherhead, Surrey, England, a corporation of the UnitedKingdom Fiied Mar. 3, 1965, Ser. No. 436,893 Claims priority,application Great Britain, Mar. 9, 1964, 9,837/64 10 Claims. (Cl.24275.43)

This invention relates to a tension sensing device whereby variations inthe tension of a travelling web may be detected, and to a method ofcontrolling the tension of a travelling web using such a tension sensingdevice.

Known methods of web tension controlling include the use of a dancingroller, which is resiliently mounted on sprung bearings and around whichpasses the tensioned web. Variations in the web tension cause variationsin the force acting on the springs fixed to the bearings and consequentvariations in the position of the dancing roller. Such a tensionregulating device is perated by means controlled by the variations inthe position of the dancing roller. Such apparatus provides anappreciable frictional resistance to the passage of the web, and has thefurther disadvantage that the speed of response to rapid variations inthe web tension is limited by the inertia of the roller.

It is an object of the present invention to provide a tension sensingdevice in which friction is minimized, and which operates tensionregulating means with a faster response to sudden variations in thetension of the web than previously known arrangements.

According to the present invention, a tension sensing device comprises afixed shaft or bar, round which a travelling web is guided, formed withan opening in its surface, said opening communicating with a source offluid under pressure through one or more restricted passages situatedwithin said shaft or bar closely adjacent to said opening and adapted toprovide a fluid cushion between the web and the shaft or bar, therebyholding the web away from the surface, and pressure detecting means incommunication with means being a part of the fluid cushion.

Two or more openings may be provided in the surface of the shaft or bar,each of said openings being connected to the source of pressure fluid byrestricted passages.

The or each opening may be connected directly to the pressure detectingmeans; alternatively one or more separate apertures may be connected tothe pressure detecting means, and be situated in the shaft or barsurface so as to communicate with the fluid cushion.

Preferably means is provided for regulating the tension in the web.

Also according to the present invention a method for controlling thetension of a travelling we-b includes subjecting the travelling web tothe action of pressure fluid, so that variations in tension in said webcause variations in the pressure of said fluid, which pressurevariations cause in turn variations in the speed of travel of, and hencetension in, said web.

The pressure detecting means may comprise a slide valve operated by thepressure of the fluid cushion acting against the thrust of an adjustablereference spring. The tension regulating means may comprise a shoe brakeadapted to inhibit movement of a roll from which the web material isunwound. Alternatively the tension regulating means may comprise a motorcontrolled by the pressure detecting means and adapted to drive thetravel ling web itself or the roller on which the web material is wound.

The invention is now described by way of example with reference to theaccompanying schematic drawings, in which:

FIGURE 1 shows a tension sensing means for use in the feed of a web ofmaterial, e.g., paper, and

FIGURE 2 shows a modified form of the shaft or bar.

Referring to FIG. 1, a web 1 of paper, sheet metal, textile or similarmaterial is led around a fixed shaft or bar 2 from a reel 3, supportedby a spindle 4 on a bracket 5. The fixed shaft or bar 2 is formed with acentral duct 6 which is connected via an external pipe 7 to a source offluid under pressure (not shown).

The duct 6 communicates through one or more restricted passageways 8,with a chamber 9 running along the shaft or bar. The chamber 9communicates with an opening in the form of a shallow recess 10 formedin the surface of the shaft or bar 2, and extending over a part of thatportion thereof over which the web 1 is trained. The chamber 9 alsocommunicates directly with a further duct 11 formed in the bar 2.

A pipe 12 connected to the duct 11 couples the tension sensing meansdescribed above to a pressure detecting device, which has the form of aslide valve. This valve comprises a cylindrical tube 13 formed with fiveequally spaced annular grooves 14a, 14b, 14c, 14d and 142 in its innersurface, inside which tube a rod 15 formed with four equally spacedlands 16 is a tight sliding fit. The lands 16 are so arranged that atany time two pairs of adjacent grooves are in communication with eachother. The pipe 12 is connected to one end of the tube 13, and a plunger17 is slidable in the valve tube 13, and is connected, through a balljoint 18, to the end of the rod 15 adjacent the tube end connected tothe pipe 12. Consequently the fluid pressure in the tube 12 acts againstthe plunger 17 and through this on the rod 15, At its other end, the rod15 is connected, through a ball joint 19, to an end member 20, slidablein the tube 13. A spring 21 lies in compression between the end member2t) and an abutment member 22 which is longitudinally adjustable in thetube 13 by means of a screw head 23.

The central annular groove is connected by a flow line 24 to a secondsource of fluid under pressure (not shown), and the two outermostgrooves 14a and 14e are connected by a line 25 to exhaust. The tworemaining grooves 14b and 14d are connected by lines 26 and 27respectively to opposite ends of a cylinder 28, in which slides a piston29. The piston 29 controls means for regulating tension in the web 1.The piston 29 operates a shoe brake 30, which is arranged to act againstan annulus 31 rotating with the reel 3, by means of levers 32.

When the apparatus is in operation, the web 1 is drawn from the reel 3,round the stationary shaft or bar 2. The pipe 7 is connected to a sourceO f fluid under pressure, and this fluid flows at an approximatelyconstant rate through the restrictions 8. The fluid then flows outbetween the web 1 and the shaft or bar 2, so that a fluid cushion isformed therebetween as indicated by the arrows 33. The frictional dragon the web is thus minimised. The thickness of the fluid cushion betweenthe web and the bar is very narrow, being normally of the.

- cushion, and in the pressure communicated through the pipe 12 to thepressure detecting means. The tension sensing device thus convertsvariations in the web tension into pressure variations in the fluid,while offering the minimum frictional resistance to the passage of theweb.

These pressure variations act through the pipe 12 against the plunger17, which is caused to move to the right asshown against the bias of thespring 21. A rise in the fluid pressure causes the valve to slide to theright so that the grooves 14a and 1419 are put in communication witheach other, as are the grooves 14c and 14d. This movement of the valveincreases fluid pressure in the line 27 which is placed in communicationwith the inlet 24, the line 26 being connected to exhaust 25. Hence thepiston 29 moves downwardly (as shown in the drawing), releasing the shoebrake and allowing the web to run freely. Conversely, a drop in the webtension leads to a drop in the fluid pressure in the pipe 12,causing-the valve to slide to the left, as shown in the drawing, so thatthe grooves 141) and 14c communicate with each other, as do the grooves14d and 142. This movement of the valve increases the pressure in theline 26' which is placed in communication with the inlet 24 while theline 27 is connected to exhaust 25. Hence the piston 29 moves upwardlyas shown in the drawing, causing the shoe brake 30 to be applied, thusretarding the web, and tending to increase its tension. The spring 21may be adjusted by the screw head 23, and thus the tension in the webmay be controlled.

When the apparatus is in operation, this method of tension control has amuch (faster response to sudden changes of the tension than previouslyused methods thus minimising the risk of breaks in the web. Also thereis only a very small frictional resistance to the passage of the webround the bar, this resistance being much less thanvwould result fromthe $1158 of any form of roller.

The choice of fluid for use in the tension sensing device depends uponthe nature of the web. For a web of paper or textile material, air isthe most suitable fluid. If, however, a metal film is passing thesensing device, it may 'be more appropriate to use a liquid, which willincrease the speed of response to tension variations. In such a casesome recirculation device would be used to prevent wastage of theliquid. In the slide valve, any suitable fluid may be used, inparticular, such a fluid as a light low viscosity oil.

The apparatus may be modified in manyrespects, though the principle ofthe method of tension control remains unchanged. The shoe brake may bereplaced by, rfor example, an electric or hydraulic motor driving thereel 3, or directly driving the web 1, and with its speed regulated bymeansconnected to and operated by the valve 13. Instead of using a slidevalve to detect the pressure variations in the pipe 12, this could bedone by any other known means, such as by using a diaphragm with asensing system attached thereto. The tension sensing device itself maybe modified from the form shown in FIG. 1 and described above. In onemodified form, two chambers each connected 'by a restriction 8 to thecentral duct 6, can be used symmetrically disposed, so that the webtravels past the opening of each. The pipe 12 then is connected to anopening along the length of the bar 2, between the openings of thechambers 9.

The fluid cushion provided between the travelling web and the surface ofthe shaft or bar in accordance with the present invention may if desiredbe generated by means of an insertion of a porous material fitted in theshaft or bar and affording the restricted passages and openings in itssurface referred to earlier. The porous material may be sintered bronzeor another sintered metal, :for example. This measure gives more evenair distribution and more uniform pressure over the main portion of theWeb, and is particularly advantageous when the web being supported iseasily flexible, as a paper web would be.

The use of a porous material insertion, which may be a sintered metal,is illustrated in FIG. 2. Here a web 51 is led around a fixed shaft orbar 52 from a reel not shown in this figure. The shaft or bar 52 has aduct 56 which is connected by a pipe 57 to a source of fluid underpressure (not shown) and which in turn leads the fluid under pressure tothe porous-material insertion 58. The latter affords restricted passagesand openings through which the fluid under pressure passes to generate afluid cushion as indicated by the arrows 59.

FIG. 2 also illustrates the use of a diaphragm to afford the pressuredetecting means. The diaphragm is shown in FIG. 2 at 60 and is mountedat the constricted end 61 of a constant-pressure fluid supply pipe 62,which is also constricted at 63, bridging a gap in the porousmaterialinsertion 58. The diaphragm 60 is thus exposed to the pressure of thefluid cushion 59 onits outer side. When the latter is relatively low,therefore, fluid from pipe 62 flows out through the constrictions 63 and61; and through an exhaust pipe 64, but when it is reiatively high thediaphragm 60 closes the constriction 61 and the pressure downstream ofconstriction 63 rises towards the full value of the pressure upstream of63. The increased pressure is transmitted by way of pipe 65 toregulating means, not shown in FIG. 2, which are actuated to reduce thetension in the web 51. The regulating means are similarly actuated toincrease the tension in the web 51 when the pressure of the fluidcushion 59 and the pressure in the pipe 65 become excessively low, thediaphragm 60 being in the nature of a flapper valve.

1 claim:

1. A tension sensing device which comprises a fixed elongated body,round which a travelling web is guided, formed with an opening in itssurface, said opening communicating with a source of fluid underpressure through at least one restricted passage situated within saidelongated body closely adjacent to said opening and being adapted toprovide a fluid cushion between the web and the surface of the elongatedbody, thereby holding the web away from the surface, and pressuredetecting means in communication with means being a part of the fluidcushion.

2. A device according to claim 1, in which at least two openings areprovided in the elongated body, each of said openings being connected tothe source of pressure fluid by a restricted passage.

3. A device according to claim 2, in which the elongated body has withinit an insertion of a porous material and this insertion affords the saidrestricted passages and openings.

4-. A device according to claim 3, in which the porous material is asintered metal.

5. A device according to claim 1, in which the opening is connected tothe pressure detecting means.

6. A device according to claim 2, having at least one aperture separatefrom the said openings, connected to the pressure detecting means andsituated in the elongated body surface so as to communicate with thefluid cushion.

7. A device according to claim 1, in which the pressure detecting meanscontrols means for regulating the tension in the travelling web.

8. A device according to claim 7, in combination with a rotatablewebyroll from which said web is unwound and travels to said elongatedbody, and in which said regulating means comprise a shoe brake adaptedto inhibit rotation of said roll.

9. A device according to claim 1 in which the pressure detecting meanscomprise a diaphragm With a sensing system attached thereto, thepressure prevailing at one of the faces of the diaphragm being thepressure of the fluid cushinn.

10. A device according to claim 1 in which said opening is in the formof a shallow recess formed in the surface of said elongated body andextends over a part of References Cited by the Examiner UNITED STATESPATENTS 2,079,268 5/1937 Wiedmann 24275.53 2,755,032 7/1956 Justus242-75.43 2,908,290 10/1959 Hamilton-Peters 251118 X FRANK J. COHEN,Primary Examiner.

0 N. L. MINTZ, Assistant Examiner.

1. A TENSION SENSING DEVICE WHICH COMPRISES A FIXED ELONGATED BODY,ROUND WHICH A TRAVELLING WEB IS GUIDED, FORMED WITH AN OPENING IN ITSSURFACE, SAID OPENING COMMUNICATING WITH A SOURCE OF FLUID UNDERPRESSURE THROUGH AT LEAST ONE RESTRICTED PASSAGE SITUATED WITHIN SAIDELONGATED BODY CLOSELY ADJACENT TO SAID OPENING AND BEING ADAPTED TOPROVIDE A FLUID CUSHION BETWEEN THE WEB AND THE SURFACE OF THE ELONGATEDBODY, THEREBY HOLDING THE WEB AWAY FROM THE SURFACE, AND PRESSUREDETECTING MEANS IN COMMUNICATION WITH MEANS BEING A PART OF THE FLUIDCUSHION.